The invention generally relates to inverted cylindrical magnetron sources and the methods of use.
The use of magnetron sputtering in the rapid deposition of metal films, reactively sputtered compound films and etching processes has found broad acceptance. The most-used type is the planar magnetron and its deposition profile and shown that the uniformity of the film thickness depends on the plasma sheath thickness and the magnetic field strength. The so-called inverted cylindrical magnetron (ICM), in which the target is a cylinder eroded by the sputtering plasma at the inner surface, is more complicated in target geometry and bonding, and hence its greater fabrication cost.
In addition, conventional ICM sources are developed mainly for single substrate deposition and have only annular end-anodes as the actual anodes. Imaginary central virtual anode (plasma with potential equal to the end-anode potential) provide electron-conducting path along axial direction without blocking deposition flux. However, such virtual anode forming along magnetic field lines is still inferior as the magnetic field lines are curved to cathode side towards two ends, and also the virtual anode is subject to operation conditions and actual hardware design. Under some ICM operation conditions, plasma impedance can be quite high such that the electrical field uniformity is not as good as that with actual anode (made of metal: very low resistance).
With conventional art, the chamber wall is electrically connected to the target as the cathode and thus electrical insulator at each end is required. Those electrical insulators are normally made of brazed ceramics-metal tubular structure, which will add alignment error and can still be subject to electrical short due to metallic deposits.
Conventional art ICM sources using metallic bonded target to copper tube is very expensive and has significant operation temperature limit due to lower melting point of bonding materials, which makes it almost impossible for high deposition rate applications. For some applications that require specific target temperature control, copper construction may lead to temperature non-uniformity due to copper's very high heat conductivity and relatively lower heat capacitance.
The prior art of ICM magnetron uses permanent magnets and has only fixed magnetic field and inherently suffers from non-uniform target erosion and related film deposition non-uniformity. Implementation of some motion mechanisms can help improve the uniformity to certain extent, but it creates hardware complexity and is still lacking easy magnetic field tunability, which cannot meet stringent requirements of high demanding applications such as ultra-precise stoichiometry control in medical device material deposition that exceeds known PVD film applications at over 1 um thickness range.
In the conventional configuration, the endcap is made of metallic component such as a cathode end flange to electrically reflect high energy electron back into plasma so that “end losses to anode” can be significantly reduced. Although the main cathode/target is sputtered, the cathode end flange should be of the same material or coated with the same target materials when contamination is not tolerable and very high purity coating is required.
Conventional coil design applies a single zone solenoid coil and suffers non-uniform magnetic flux density along the axial direction. Multiple solenoid coils in series suffer from non-smooth magnetic field transition profiles. And conventional ICM magnetron sputtering has fixed substrate-to-target distance per equipment design and it is normally not an available process-tuning knob.
The present invention attempts to solve these problems as well as others in order to meet stringent requirements of high demanding applications.